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68dc0745 | 1 | =head1 NAME |
2 | ||
d92eb7b0 | 3 | perlfaq3 - Programming Tools ($Revision: 1.38 $, $Date: 1999/05/23 16:08:30 $) |
68dc0745 | 4 | |
5 | =head1 DESCRIPTION | |
6 | ||
7 | This section of the FAQ answers questions related to programmer tools | |
8 | and programming support. | |
9 | ||
10 | =head2 How do I do (anything)? | |
11 | ||
12 | Have you looked at CPAN (see L<perlfaq2>)? The chances are that | |
13 | someone has already written a module that can solve your problem. | |
46fc3d4c | 14 | Have you read the appropriate man pages? Here's a brief index: |
68dc0745 | 15 | |
5a964f20 TC |
16 | Basics perldata, perlvar, perlsyn, perlop, perlsub |
17 | Execution perlrun, perldebug | |
18 | Functions perlfunc | |
68dc0745 | 19 | Objects perlref, perlmod, perlobj, perltie |
20 | Data Structures perlref, perllol, perldsc | |
f102b883 | 21 | Modules perlmod, perlmodlib, perlsub |
d92eb7b0 | 22 | Regexes perlre, perlfunc, perlop, perllocale |
68dc0745 | 23 | Moving to perl5 perltrap, perl |
24 | Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed | |
25 | Various http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html | |
26 | (not a man-page but still useful) | |
27 | ||
87275199 | 28 | A crude table of contents for the Perl man page set is found in L<perltoc>. |
68dc0745 | 29 | |
30 | =head2 How can I use Perl interactively? | |
31 | ||
32 | The typical approach uses the Perl debugger, described in the | |
92c2ed05 | 33 | perldebug(1) man page, on an ``empty'' program, like this: |
68dc0745 | 34 | |
35 | perl -de 42 | |
36 | ||
37 | Now just type in any legal Perl code, and it will be immediately | |
38 | evaluated. You can also examine the symbol table, get stack | |
39 | backtraces, check variable values, set breakpoints, and other | |
92c2ed05 | 40 | operations typically found in symbolic debuggers. |
68dc0745 | 41 | |
42 | =head2 Is there a Perl shell? | |
43 | ||
87275199 GS |
44 | In general, no. The Shell.pm module (distributed with Perl) makes |
45 | Perl try commands which aren't part of the Perl language as shell | |
68dc0745 | 46 | commands. perlsh from the source distribution is simplistic and |
47 | uninteresting, but may still be what you want. | |
48 | ||
49 | =head2 How do I debug my Perl programs? | |
50 | ||
92c2ed05 | 51 | Have you used C<-w>? It enables warnings for dubious practices. |
68dc0745 | 52 | |
92c2ed05 GS |
53 | Have you tried C<use strict>? It prevents you from using symbolic |
54 | references, makes you predeclare any subroutines that you call as bare | |
55 | words, and (probably most importantly) forces you to predeclare your | |
77ca0c92 | 56 | variables with C<my> or C<our> or C<use vars>. |
68dc0745 | 57 | |
92c2ed05 GS |
58 | Did you check the returns of each and every system call? The operating |
59 | system (and thus Perl) tells you whether they worked or not, and if not | |
60 | why. | |
68dc0745 | 61 | |
92c2ed05 GS |
62 | open(FH, "> /etc/cantwrite") |
63 | or die "Couldn't write to /etc/cantwrite: $!\n"; | |
68dc0745 | 64 | |
92c2ed05 GS |
65 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
66 | programmers, and even has sections for those of you who are upgrading | |
67 | from languages like I<awk> and I<C>. | |
68 | ||
69 | Have you tried the Perl debugger, described in L<perldebug>? You can | |
70 | step through your program and see what it's doing and thus work out | |
71 | why what it's doing isn't what it should be doing. | |
68dc0745 | 72 | |
73 | =head2 How do I profile my Perl programs? | |
74 | ||
75 | You should get the Devel::DProf module from CPAN, and also use | |
76 | Benchmark.pm from the standard distribution. Benchmark lets you time | |
77 | specific portions of your code, while Devel::DProf gives detailed | |
78 | breakdowns of where your code spends its time. | |
79 | ||
92c2ed05 GS |
80 | Here's a sample use of Benchmark: |
81 | ||
82 | use Benchmark; | |
83 | ||
84 | @junk = `cat /etc/motd`; | |
85 | $count = 10_000; | |
86 | ||
87 | timethese($count, { | |
88 | 'map' => sub { my @a = @junk; | |
89 | map { s/a/b/ } @a; | |
90 | return @a | |
91 | }, | |
92 | 'for' => sub { my @a = @junk; | |
93 | local $_; | |
94 | for (@a) { s/a/b/ }; | |
95 | return @a }, | |
96 | }); | |
97 | ||
98 | This is what it prints (on one machine--your results will be dependent | |
99 | on your hardware, operating system, and the load on your machine): | |
100 | ||
101 | Benchmark: timing 10000 iterations of for, map... | |
102 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) | |
103 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) | |
104 | ||
65acb1b1 TC |
105 | Be aware that a good benchmark is very hard to write. It only tests the |
106 | data you give it, and really proves little about differing complexities | |
107 | of contrasting algorithms. | |
108 | ||
68dc0745 | 109 | =head2 How do I cross-reference my Perl programs? |
110 | ||
111 | The B::Xref module, shipped with the new, alpha-release Perl compiler | |
5a964f20 TC |
112 | (not the general distribution prior to the 5.005 release), can be used |
113 | to generate cross-reference reports for Perl programs. | |
68dc0745 | 114 | |
c8db1d39 | 115 | perl -MO=Xref[,OPTIONS] scriptname.plx |
68dc0745 | 116 | |
117 | =head2 Is there a pretty-printer (formatter) for Perl? | |
118 | ||
92c2ed05 GS |
119 | There is no program that will reformat Perl as much as indent(1) does |
120 | for C. The complex feedback between the scanner and the parser (this | |
121 | feedback is what confuses the vgrind and emacs programs) makes it | |
68dc0745 | 122 | challenging at best to write a stand-alone Perl parser. |
123 | ||
124 | Of course, if you simply follow the guidelines in L<perlstyle>, you | |
92c2ed05 GS |
125 | shouldn't need to reformat. The habit of formatting your code as you |
126 | write it will help prevent bugs. Your editor can and should help you | |
127 | with this. The perl-mode for emacs can provide a remarkable amount of | |
128 | help with most (but not all) code, and even less programmable editors | |
65acb1b1 TC |
129 | can provide significant assistance. Tom swears by the following |
130 | settings in vi and its clones: | |
131 | ||
132 | set ai sw=4 | |
d92eb7b0 | 133 | map! ^O {^M}^[O^T |
65acb1b1 TC |
134 | |
135 | Now put that in your F<.exrc> file (replacing the caret characters | |
136 | with control characters) and away you go. In insert mode, ^T is | |
137 | for indenting, ^D is for undenting, and ^O is for blockdenting -- | |
138 | as it were. If you haven't used the last one, you're missing | |
139 | a lot. A more complete example, with comments, can be found at | |
140 | http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz | |
92c2ed05 | 141 | |
65acb1b1 | 142 | If you are used to using the I<vgrind> program for printing out nice code |
92c2ed05 | 143 | to a laser printer, you can take a stab at this using |
68dc0745 | 144 | http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the |
145 | results are not particularly satisfying for sophisticated code. | |
146 | ||
87275199 | 147 | The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things |
65acb1b1 TC |
148 | related to generating nicely printed output of documents. |
149 | ||
d92eb7b0 | 150 | =head2 Is there a ctags for Perl? |
68dc0745 | 151 | |
d92eb7b0 | 152 | There's a simple one at |
68dc0745 | 153 | http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do |
65acb1b1 TC |
154 | the trick. And if not, it's easy to hack into what you want. |
155 | ||
156 | =head2 Is there an IDE or Windows Perl Editor? | |
157 | ||
d92eb7b0 GS |
158 | If you're on Unix, you already have an IDE -- Unix itself. This powerful |
159 | IDE derives from its interoperability, flexibility, and configurability. | |
160 | If you really want to get a feel for Unix-qua-IDE, the best thing to do | |
161 | is to find some high-powered programmer whose native language is Unix. | |
162 | Find someone who has been at this for many years, and just sit back | |
163 | and watch them at work. They have created their own IDE, one that | |
164 | suits their own tastes and aptitudes. Quietly observe them edit files, | |
165 | move them around, compile them, debug them, test them, etc. The entire | |
166 | development *is* integrated, like a top-of-the-line German sports car: | |
167 | functional, powerful, and elegant. You will be absolutely astonished | |
168 | at the speed and ease exhibited by the native speaker of Unix in his | |
169 | home territory. The art and skill of a virtuoso can only be seen to be | |
170 | believed. That is the path to mastery -- all these cobbled little IDEs | |
171 | are expensive toys designed to sell a flashy demo using cheap tricks, | |
172 | and being optimized for immediate but shallow understanding rather than | |
173 | enduring use, are but a dim palimpsest of real tools. | |
174 | ||
175 | In short, you just have to learn the toolbox. However, if you're not | |
176 | on Unix, then your vendor probably didn't bother to provide you with | |
177 | a proper toolbox on the so-called complete system that you forked out | |
178 | your hard-earned cash on. | |
179 | ||
180 | PerlBuilder (XXX URL to follow) is an integrated development environment | |
181 | for Windows that supports Perl development. Perl programs are just plain | |
182 | text, though, so you could download emacs for Windows (???) or a vi clone | |
87275199 | 183 | (vim) which runs on for win32 (http://www.cs.vu.nl/%7Etmgil/vi.html). |
d92eb7b0 GS |
184 | If you're transferring Windows files to Unix, be sure to transfer in |
185 | ASCII mode so the ends of lines are appropriately mangled. | |
68dc0745 | 186 | |
187 | =head2 Where can I get Perl macros for vi? | |
188 | ||
189 | For a complete version of Tom Christiansen's vi configuration file, | |
65acb1b1 | 190 | see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz, |
5a964f20 TC |
191 | the standard benchmark file for vi emulators. This runs best with nvi, |
192 | the current version of vi out of Berkeley, which incidentally can be built | |
193 | with an embedded Perl interpreter -- see http://www.perl.com/CPAN/src/misc. | |
68dc0745 | 194 | |
195 | =head2 Where can I get perl-mode for emacs? | |
196 | ||
197 | Since Emacs version 19 patchlevel 22 or so, there have been both a | |
87275199 | 198 | perl-mode.el and support for the Perl debugger built in. These should |
68dc0745 | 199 | come with the standard Emacs 19 distribution. |
200 | ||
87275199 | 201 | In the Perl source directory, you'll find a directory called "emacs", |
68dc0745 | 202 | which contains a cperl-mode that color-codes keywords, provides |
203 | context-sensitive help, and other nifty things. | |
204 | ||
92c2ed05 | 205 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
d92eb7b0 | 206 | (single quote), and mess up the indentation and highlighting. You |
65acb1b1 | 207 | are probably using C<"main::foo"> in new Perl code anyway, so this |
92c2ed05 | 208 | shouldn't be an issue. |
68dc0745 | 209 | |
210 | =head2 How can I use curses with Perl? | |
211 | ||
212 | The Curses module from CPAN provides a dynamically loadable object | |
5a964f20 TC |
213 | module interface to a curses library. A small demo can be found at the |
214 | directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep; | |
215 | this program repeats a command and updates the screen as needed, rendering | |
216 | B<rep ps axu> similar to B<top>. | |
68dc0745 | 217 | |
218 | =head2 How can I use X or Tk with Perl? | |
219 | ||
5a964f20 TC |
220 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
221 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface | |
222 | to the Athena Widget set. Both are available from CPAN. See the | |
223 | directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/ | |
68dc0745 | 224 | |
92c2ed05 | 225 | Invaluable for Perl/Tk programming are: the Perl/Tk FAQ at |
87275199 | 226 | http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
92c2ed05 GS |
227 | Guide available at |
228 | http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the | |
229 | online manpages at | |
87275199 | 230 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . |
92c2ed05 | 231 | |
68dc0745 | 232 | =head2 How can I generate simple menus without using CGI or Tk? |
233 | ||
234 | The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz | |
235 | module, which is curses-based, can help with this. | |
236 | ||
68dc0745 | 237 | =head2 What is undump? |
238 | ||
239 | See the next questions. | |
240 | ||
241 | =head2 How can I make my Perl program run faster? | |
242 | ||
92c2ed05 GS |
243 | The best way to do this is to come up with a better algorithm. This |
244 | can often make a dramatic difference. Chapter 8 in the Camel has some | |
245 | efficiency tips in it you might want to look at. Jon Bentley's book | |
246 | ``Programming Pearls'' (that's not a misspelling!) has some good tips | |
247 | on optimization, too. Advice on benchmarking boils down to: benchmark | |
248 | and profile to make sure you're optimizing the right part, look for | |
249 | better algorithms instead of microtuning your code, and when all else | |
250 | fails consider just buying faster hardware. | |
68dc0745 | 251 | |
92c2ed05 | 252 | A different approach is to autoload seldom-used Perl code. See the |
68dc0745 | 253 | AutoSplit and AutoLoader modules in the standard distribution for |
254 | that. Or you could locate the bottleneck and think about writing just | |
255 | that part in C, the way we used to take bottlenecks in C code and | |
256 | write them in assembler. Similar to rewriting in C is the use of | |
257 | modules that have critical sections written in C (for instance, the | |
258 | PDL module from CPAN). | |
259 | ||
260 | In some cases, it may be worth it to use the backend compiler to | |
261 | produce byte code (saving compilation time) or compile into C, which | |
262 | will certainly save compilation time and sometimes a small amount (but | |
263 | not much) execution time. See the question about compiling your Perl | |
92c2ed05 GS |
264 | programs for more on the compiler--the wins aren't as obvious as you'd |
265 | hope. | |
68dc0745 | 266 | |
92c2ed05 | 267 | If you're currently linking your perl executable to a shared I<libc.so>, |
68dc0745 | 268 | you can often gain a 10-25% performance benefit by rebuilding it to |
269 | link with a static libc.a instead. This will make a bigger perl | |
270 | executable, but your Perl programs (and programmers) may thank you for | |
271 | it. See the F<INSTALL> file in the source distribution for more | |
272 | information. | |
273 | ||
274 | Unsubstantiated reports allege that Perl interpreters that use sfio | |
87275199 | 275 | outperform those that don't (for I/O intensive applications). To try |
68dc0745 | 276 | this, see the F<INSTALL> file in the source distribution, especially |
87275199 | 277 | the ``Selecting File I/O mechanisms'' section. |
68dc0745 | 278 | |
279 | The undump program was an old attempt to speed up your Perl program | |
280 | by storing the already-compiled form to disk. This is no longer | |
281 | a viable option, as it only worked on a few architectures, and | |
282 | wasn't a good solution anyway. | |
283 | ||
284 | =head2 How can I make my Perl program take less memory? | |
285 | ||
286 | When it comes to time-space tradeoffs, Perl nearly always prefers to | |
287 | throw memory at a problem. Scalars in Perl use more memory than | |
65acb1b1 | 288 | strings in C, arrays take more than that, and hashes use even more. While |
68dc0745 | 289 | there's still a lot to be done, recent releases have been addressing |
290 | these issues. For example, as of 5.004, duplicate hash keys are | |
291 | shared amongst all hashes using them, so require no reallocation. | |
292 | ||
293 | In some cases, using substr() or vec() to simulate arrays can be | |
294 | highly beneficial. For example, an array of a thousand booleans will | |
295 | take at least 20,000 bytes of space, but it can be turned into one | |
296 | 125-byte bit vector for a considerable memory savings. The standard | |
297 | Tie::SubstrHash module can also help for certain types of data | |
298 | structure. If you're working with specialist data structures | |
299 | (matrices, for instance) modules that implement these in C may use | |
300 | less memory than equivalent Perl modules. | |
301 | ||
302 | Another thing to try is learning whether your Perl was compiled with | |
54310121 | 303 | the system malloc or with Perl's builtin malloc. Whichever one it |
68dc0745 | 304 | is, try using the other one and see whether this makes a difference. |
305 | Information about malloc is in the F<INSTALL> file in the source | |
306 | distribution. You can find out whether you are using perl's malloc by | |
307 | typing C<perl -V:usemymalloc>. | |
308 | ||
309 | =head2 Is it unsafe to return a pointer to local data? | |
310 | ||
311 | No, Perl's garbage collection system takes care of this. | |
312 | ||
313 | sub makeone { | |
314 | my @a = ( 1 .. 10 ); | |
315 | return \@a; | |
316 | } | |
317 | ||
318 | for $i ( 1 .. 10 ) { | |
319 | push @many, makeone(); | |
320 | } | |
321 | ||
322 | print $many[4][5], "\n"; | |
323 | ||
324 | print "@many\n"; | |
325 | ||
326 | =head2 How can I free an array or hash so my program shrinks? | |
327 | ||
c8db1d39 TC |
328 | You can't. On most operating systems, memory allocated to a program |
329 | can never be returned to the system. That's why long-running programs | |
65acb1b1 TC |
330 | sometimes re-exec themselves. Some operating systems (notably, |
331 | FreeBSD and Linux) allegedly reclaim large chunks of memory that is no | |
332 | longer used, but it doesn't appear to happen with Perl (yet). The Mac | |
333 | appears to be the only platform that will reliably (albeit, slowly) | |
334 | return memory to the OS. | |
335 | ||
336 | We've had reports that on Linux (Redhat 5.1) on Intel, C<undef | |
337 | $scalar> will return memory to the system, while on Solaris 2.6 it | |
338 | won't. In general, try it yourself and see. | |
68dc0745 | 339 | |
340 | However, judicious use of my() on your variables will help make sure | |
341 | that they go out of scope so that Perl can free up their storage for | |
92c2ed05 | 342 | use in other parts of your program. A global variable, of course, never |
68dc0745 | 343 | goes out of scope, so you can't get its space automatically reclaimed, |
344 | although undef()ing and/or delete()ing it will achieve the same effect. | |
46fc3d4c | 345 | In general, memory allocation and de-allocation isn't something you can |
68dc0745 | 346 | or should be worrying about much in Perl, but even this capability |
347 | (preallocation of data types) is in the works. | |
348 | ||
349 | =head2 How can I make my CGI script more efficient? | |
350 | ||
351 | Beyond the normal measures described to make general Perl programs | |
352 | faster or smaller, a CGI program has additional issues. It may be run | |
353 | several times per second. Given that each time it runs it will need | |
46fc3d4c | 354 | to be re-compiled and will often allocate a megabyte or more of system |
68dc0745 | 355 | memory, this can be a killer. Compiling into C B<isn't going to help |
46fc3d4c | 356 | you> because the process start-up overhead is where the bottleneck is. |
68dc0745 | 357 | |
92c2ed05 GS |
358 | There are two popular ways to avoid this overhead. One solution |
359 | involves running the Apache HTTP server (available from | |
68dc0745 | 360 | http://www.apache.org/) with either of the mod_perl or mod_fastcgi |
92c2ed05 GS |
361 | plugin modules. |
362 | ||
363 | With mod_perl and the Apache::Registry module (distributed with | |
364 | mod_perl), httpd will run with an embedded Perl interpreter which | |
365 | pre-compiles your script and then executes it within the same address | |
366 | space without forking. The Apache extension also gives Perl access to | |
367 | the internal server API, so modules written in Perl can do just about | |
368 | anything a module written in C can. For more on mod_perl, see | |
369 | http://perl.apache.org/ | |
370 | ||
65acb1b1 | 371 | With the FCGI module (from CPAN) and the mod_fastcgi |
87275199 GS |
372 | module (available from http://www.fastcgi.com/) each of your Perl |
373 | programs becomes a permanent CGI daemon process. | |
68dc0745 | 374 | |
375 | Both of these solutions can have far-reaching effects on your system | |
87275199 | 376 | and on the way you write your CGI programs, so investigate them with |
68dc0745 | 377 | care. |
378 | ||
92c2ed05 | 379 | See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
5a964f20 | 380 | |
65acb1b1 | 381 | A non-free, commercial product, ``The Velocity Engine for Perl'', |
d92eb7b0 | 382 | (http://www.binevolve.com/ or http://www.binevolve.com/bine/vep) might |
c8db1d39 | 383 | also be worth looking at. It will allow you to increase the performance |
87275199 GS |
384 | of your Perl programs, up to 25 times faster than normal CGI Perl by |
385 | running in persistent Perl mode, or 4 to 5 times faster without any | |
386 | modification to your existing CGI programs. Fully functional evaluation | |
c8db1d39 TC |
387 | copies are available from the web site. |
388 | ||
68dc0745 | 389 | =head2 How can I hide the source for my Perl program? |
390 | ||
391 | Delete it. :-) Seriously, there are a number of (mostly | |
92c2ed05 | 392 | unsatisfactory) solutions with varying levels of ``security''. |
68dc0745 | 393 | |
394 | First of all, however, you I<can't> take away read permission, because | |
395 | the source code has to be readable in order to be compiled and | |
396 | interpreted. (That doesn't mean that a CGI script's source is | |
92c2ed05 GS |
397 | readable by people on the web, though, only by people with access to |
398 | the filesystem) So you have to leave the permissions at the socially | |
399 | friendly 0755 level. | |
68dc0745 | 400 | |
401 | Some people regard this as a security problem. If your program does | |
402 | insecure things, and relies on people not knowing how to exploit those | |
403 | insecurities, it is not secure. It is often possible for someone to | |
404 | determine the insecure things and exploit them without viewing the | |
405 | source. Security through obscurity, the name for hiding your bugs | |
406 | instead of fixing them, is little security indeed. | |
407 | ||
92c2ed05 | 408 | You can try using encryption via source filters (Filter::* from CPAN), |
65acb1b1 TC |
409 | but any decent programmer will be able to decrypt it. You can try using |
410 | the byte code compiler and interpreter described below, but the curious | |
411 | might still be able to de-compile it. You can try using the native-code | |
412 | compiler described below, but crackers might be able to disassemble it. | |
413 | These pose varying degrees of difficulty to people wanting to get at | |
414 | your code, but none can definitively conceal it (this is true of every | |
68dc0745 | 415 | language, not just Perl). |
416 | ||
417 | If you're concerned about people profiting from your code, then the | |
d92eb7b0 | 418 | bottom line is that nothing but a restrictive license will give you |
68dc0745 | 419 | legal security. License your software and pepper it with threatening |
92c2ed05 | 420 | statements like ``This is unpublished proprietary software of XYZ Corp. |
68dc0745 | 421 | Your access to it does not give you permission to use it blah blah |
92c2ed05 | 422 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
d92eb7b0 | 423 | you want to be sure your license's wording will stand up in court. |
68dc0745 | 424 | |
54310121 | 425 | =head2 How can I compile my Perl program into byte code or C? |
68dc0745 | 426 | |
427 | Malcolm Beattie has written a multifunction backend compiler, | |
5e3006a4 GS |
428 | available from CPAN, that can do both these things. It is included |
429 | in the perl5.005 release, but is still considered experimental. | |
430 | This means it's fun to play with if you're a programmer but not | |
431 | really for people looking for turn-key solutions. | |
68dc0745 | 432 | |
92c2ed05 GS |
433 | Merely compiling into C does not in and of itself guarantee that your |
434 | code will run very much faster. That's because except for lucky cases | |
435 | where a lot of native type inferencing is possible, the normal Perl | |
436 | run time system is still present and so your program will take just as | |
437 | long to run and be just as big. Most programs save little more than | |
438 | compilation time, leaving execution no more than 10-30% faster. A few | |
439 | rare programs actually benefit significantly (like several times | |
440 | faster), but this takes some tweaking of your code. | |
68dc0745 | 441 | |
68dc0745 | 442 | You'll probably be astonished to learn that the current version of the |
443 | compiler generates a compiled form of your script whose executable is | |
444 | just as big as the original perl executable, and then some. That's | |
445 | because as currently written, all programs are prepared for a full | |
446 | eval() statement. You can tremendously reduce this cost by building a | |
92c2ed05 | 447 | shared I<libperl.so> library and linking against that. See the |
87275199 | 448 | F<INSTALL> podfile in the Perl source distribution for details. If |
d92eb7b0 | 449 | you link your main perl binary with this, it will make it minuscule. |
92c2ed05 | 450 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
68dc0745 | 451 | size! |
452 | ||
5a964f20 TC |
453 | In general, the compiler will do nothing to make a Perl program smaller, |
454 | faster, more portable, or more secure. In fact, it will usually hurt | |
455 | all of those. The executable will be bigger, your VM system may take | |
456 | longer to load the whole thing, the binary is fragile and hard to fix, | |
457 | and compilation never stopped software piracy in the form of crackers, | |
458 | viruses, or bootleggers. The real advantage of the compiler is merely | |
459 | packaging, and once you see the size of what it makes (well, unless | |
460 | you use a shared I<libperl.so>), you'll probably want a complete | |
5e3006a4 | 461 | Perl install anyway. |
5a964f20 | 462 | |
65acb1b1 TC |
463 | =head2 How can I compile Perl into Java? |
464 | ||
465 | You can't. Not yet, anyway. You can integrate Java and Perl with the | |
466 | Perl Resource Kit from O'Reilly and Associates. See | |
467 | http://www.oreilly.com/catalog/prkunix/ for more information. | |
87275199 | 468 | The Java interface will be supported in the core 5.6 release |
65acb1b1 TC |
469 | of Perl. |
470 | ||
92c2ed05 | 471 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
68dc0745 | 472 | |
473 | For OS/2 just use | |
474 | ||
475 | extproc perl -S -your_switches | |
476 | ||
477 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's | |
46fc3d4c | 478 | `extproc' handling). For DOS one should first invent a corresponding |
68dc0745 | 479 | batch file, and codify it in C<ALTERNATIVE_SHEBANG> (see the |
480 | F<INSTALL> file in the source distribution for more information). | |
481 | ||
92c2ed05 GS |
482 | The Win95/NT installation, when using the ActiveState port of Perl, |
483 | will modify the Registry to associate the C<.pl> extension with the | |
d92eb7b0 GS |
484 | perl interpreter. If you install another port, perhaps even building |
485 | your own Win95/NT Perl from the standard sources by using a Windows port | |
486 | of gcc (e.g., with cygwin32 or mingw32), then you'll have to modify | |
487 | the Registry yourself. In addition to associating C<.pl> with the | |
488 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them | |
489 | run the program C<install-linux.pl> merely by typing C<install-linux>. | |
68dc0745 | 490 | |
87275199 GS |
491 | Macintosh Perl programs will have the appropriate Creator and |
492 | Type, so that double-clicking them will invoke the Perl application. | |
68dc0745 | 493 | |
494 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just | |
495 | throw the perl interpreter into your cgi-bin directory, in order to | |
87275199 | 496 | get your programs working for a web server. This is an EXTREMELY big |
68dc0745 | 497 | security risk. Take the time to figure out how to do it correctly. |
498 | ||
87275199 | 499 | =head2 Can I write useful Perl programs on the command line? |
68dc0745 | 500 | |
501 | Yes. Read L<perlrun> for more information. Some examples follow. | |
502 | (These assume standard Unix shell quoting rules.) | |
503 | ||
504 | # sum first and last fields | |
5a964f20 | 505 | perl -lane 'print $F[0] + $F[-1]' * |
68dc0745 | 506 | |
507 | # identify text files | |
508 | perl -le 'for(@ARGV) {print if -f && -T _}' * | |
509 | ||
5a964f20 | 510 | # remove (most) comments from C program |
68dc0745 | 511 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
512 | ||
513 | # make file a month younger than today, defeating reaper daemons | |
514 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * | |
515 | ||
516 | # find first unused uid | |
517 | perl -le '$i++ while getpwuid($i); print $i' | |
518 | ||
519 | # display reasonable manpath | |
520 | echo $PATH | perl -nl -072 -e ' | |
521 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' | |
522 | ||
87275199 | 523 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
68dc0745 | 524 | |
87275199 | 525 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
68dc0745 | 526 | |
527 | The problem is usually that the command interpreters on those systems | |
528 | have rather different ideas about quoting than the Unix shells under | |
529 | which the one-liners were created. On some systems, you may have to | |
530 | change single-quotes to double ones, which you must I<NOT> do on Unix | |
531 | or Plan9 systems. You might also have to change a single % to a %%. | |
532 | ||
533 | For example: | |
534 | ||
535 | # Unix | |
536 | perl -e 'print "Hello world\n"' | |
537 | ||
46fc3d4c | 538 | # DOS, etc. |
68dc0745 | 539 | perl -e "print \"Hello world\n\"" |
540 | ||
46fc3d4c | 541 | # Mac |
68dc0745 | 542 | print "Hello world\n" |
543 | (then Run "Myscript" or Shift-Command-R) | |
544 | ||
545 | # VMS | |
546 | perl -e "print ""Hello world\n""" | |
547 | ||
92c2ed05 GS |
548 | The problem is that none of this is reliable: it depends on the |
549 | command interpreter. Under Unix, the first two often work. Under DOS, | |
550 | it's entirely possible neither works. If 4DOS was the command shell, | |
551 | you'd probably have better luck like this: | |
68dc0745 | 552 | |
553 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" | |
554 | ||
46fc3d4c | 555 | Under the Mac, it depends which environment you are using. The MacPerl |
68dc0745 | 556 | shell, or MPW, is much like Unix shells in its support for several |
46fc3d4c | 557 | quoting variants, except that it makes free use of the Mac's non-ASCII |
68dc0745 | 558 | characters as control characters. |
559 | ||
65acb1b1 TC |
560 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
561 | quotes', and `backticks`, may make one-liners easier to write. | |
562 | ||
92c2ed05 GS |
563 | There is no general solution to all of this. It is a mess, pure and |
564 | simple. Sucks to be away from Unix, huh? :-) | |
68dc0745 | 565 | |
566 | [Some of this answer was contributed by Kenneth Albanowski.] | |
567 | ||
568 | =head2 Where can I learn about CGI or Web programming in Perl? | |
569 | ||
570 | For modules, get the CGI or LWP modules from CPAN. For textbooks, | |
571 | see the two especially dedicated to web stuff in the question on | |
92c2ed05 GS |
572 | books. For problems and questions related to the web, like ``Why |
573 | do I get 500 Errors'' or ``Why doesn't it run from the browser right | |
574 | when it runs fine on the command line'', see these sources: | |
68dc0745 | 575 | |
5a964f20 TC |
576 | WWW Security FAQ |
577 | http://www.w3.org/Security/Faq/ | |
68dc0745 | 578 | |
5a964f20 TC |
579 | Web FAQ |
580 | http://www.boutell.com/faq/ | |
68dc0745 | 581 | |
5a964f20 | 582 | CGI FAQ |
d92eb7b0 | 583 | http://www.webthing.com/page.cgi/cgifaq |
68dc0745 | 584 | |
5a964f20 TC |
585 | HTTP Spec |
586 | http://www.w3.org/pub/WWW/Protocols/HTTP/ | |
587 | ||
588 | HTML Spec | |
589 | http://www.w3.org/TR/REC-html40/ | |
590 | http://www.w3.org/pub/WWW/MarkUp/ | |
591 | ||
592 | CGI Spec | |
593 | http://www.w3.org/CGI/ | |
594 | ||
595 | CGI Security FAQ | |
596 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt | |
68dc0745 | 597 | |
68dc0745 | 598 | |
599 | =head2 Where can I learn about object-oriented Perl programming? | |
600 | ||
87275199 | 601 | A good place to start is L<perltoot>, and you can use L<perlobj> and |
68dc0745 | 602 | L<perlbot> for reference. Perltoot didn't come out until the 5.004 |
603 | release, but you can get a copy (in pod, html, or postscript) from | |
604 | http://www.perl.com/CPAN/doc/FMTEYEWTK/ . | |
605 | ||
606 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] | |
607 | ||
608 | If you want to call C from Perl, start with L<perlxstut>, | |
609 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to | |
610 | call Perl from C, then read L<perlembed>, L<perlcall>, and | |
611 | L<perlguts>. Don't forget that you can learn a lot from looking at | |
612 | how the authors of existing extension modules wrote their code and | |
613 | solved their problems. | |
614 | ||
615 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in | |
616 | my C program, what am I doing wrong? | |
617 | ||
618 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If | |
619 | the tests pass, read the pods again and again and again. If they | |
87275199 | 620 | fail, see L<perlbug> and send a bug report with the output of |
68dc0745 | 621 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
622 | ||
623 | =head2 When I tried to run my script, I got this message. What does it | |
624 | mean? | |
625 | ||
87275199 GS |
626 | A complete list of Perl's error messages and warnings with explanatory |
627 | text can be found in L<perldiag>. You can also use the splain program | |
628 | (distributed with Perl) to explain the error messages: | |
68dc0745 | 629 | |
630 | perl program 2>diag.out | |
631 | splain [-v] [-p] diag.out | |
632 | ||
633 | or change your program to explain the messages for you: | |
634 | ||
635 | use diagnostics; | |
636 | ||
637 | or | |
638 | ||
639 | use diagnostics -verbose; | |
640 | ||
641 | =head2 What's MakeMaker? | |
642 | ||
87275199 | 643 | This module (part of the standard Perl distribution) is designed to |
68dc0745 | 644 | write a Makefile for an extension module from a Makefile.PL. For more |
645 | information, see L<ExtUtils::MakeMaker>. | |
646 | ||
647 | =head1 AUTHOR AND COPYRIGHT | |
648 | ||
65acb1b1 | 649 | Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. |
5a964f20 TC |
650 | All rights reserved. |
651 | ||
c8db1d39 | 652 | When included as an integrated part of the Standard Distribution |
d92eb7b0 GS |
653 | of Perl or of its documentation (printed or otherwise), this works is |
654 | covered under Perl's Artistic License. For separate distributions of | |
c8db1d39 TC |
655 | all or part of this FAQ outside of that, see L<perlfaq>. |
656 | ||
87275199 | 657 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 TC |
658 | domain. You are permitted and encouraged to use this code and any |
659 | derivatives thereof in your own programs for fun or for profit as you | |
660 | see fit. A simple comment in the code giving credit to the FAQ would | |
661 | be courteous but is not required. |